I cut my plants back about a month ago. But it's cooling off now, just a bit, and most of the ones I'd like to have grow back are going strong.
Particularly the containers of ornamental grasses. They have grown at least a foot!
So don't go too crazy cutting back the dead foliage if you have many winter months. The birds will appreciate the cover you leave for them.
Cut back the following perennials in the fall
Iris: Trimming back the leaves at the right time keeps the plant healthy and attractive, while still allowing the iris to replenish the nutrient stores in its rhizomatous root system.
It is best to cut back bee balm because it has a tendency to mildew
Phlox: It also has a tendency to mildew.
Prune the daylilies. If you don't prune daylilies, you will get new growth mixed in with old come spring.
Once the green leaves start to die, take off the foliage.
Blanket Flower: Cut this plant back in the fall because it helps the plant to come back more vigorous come spring/summer.
Wait until spring to cut these perennials back
It's best to prune the butterfly bush in early spring.
Coneflowers: Leave these plants alone until spring so the birds can feast on the seed throughout winter.
Astilbe: This plant will give you green during winter, so wait to cut this one back until spring.
Dianthus: In warm climates, dianthus will give you blooms in both spring and fall. And they look good throughout winter.